The goal of the proposed research is to identify novel mechanisms that regulate type 2 innate lymphoid cells (ILC2). ILC2 are a recently discovered population of lineage-negative lymphocytes that produce Th2 cytokines in response to epithelial cytokines IL-33 and TSLP. ILC2 contribute to an asthma phenotype in animal models and are present in human lungs. Specifically, we hypothesize that the RNA-binding protein RBM3 controls human and mouse ILC2 Th2 cytokine production and innate type 2 lung responses through Th2 cytokine mRNA stabilization. We will administer allergen, IL-33, and TSLP challenges to the airways of WT and RBM3 knockout mice and assess lung ILC2 Th2 cytokine production and proliferation, as well as levels of BAL eosinophils, epithelial mucus production, peribronchial infiltration and airway hyperresponsiveness. We will also perform ILC2 adoptive transfer studies and generate RBM3 deficient IL-13 reporter mice to define the role of RBM3 in ILC2 during allergen, IL-33, and TSLP-induced airway inflammation. We will perform in vitro studies with purified ILC2 from WT and RBM3 knockout mice as well as human RMB3 siRNA knockdown ILC2 stimulated with IL-33 and TSLP and assess levels of ILC2 Th2 cytokine production and proliferation. Further, we will perform mRNA stability assays to determine whether RBM3 controls ILC2 function by stabilizing Th2 cytokine mRNAs. We expect to find that RMB3 promotes ILC2 Th2 cytokine mRNA stability and controls ILC2 Th2 cytokine production in vitro and in vivo. The novelty of the proposed studies includes use of novel reagents (RBM3-/-, RBM3-/-RAG2-/-, and RBM3-/-/YFP-IL-13 reporter mice) and uncovering a novel pathway (RNA binding protein) regulating a recently discovered cell type (ILC2) that contributes to allergic inflammation. Importantly, the discovery of molecules that regulate ILC2 function may reveal novel therapeutic targets to reduce ILC2 activation in asthma and allergic disease.